I took the pinion and vacuum shifter apart this weekend. Getting the pinion nut off was a challenge- i had to heat the nut with the torch almot cherry red before it decided to start turning, and a bearing puller was needed to get the yoke and double cone bearings off.
As I expected, the pinion seal was worn out and the seal lip was non-existent. A deep groove has been worn into the driveshaft yoke, but I am going to move the seal forward into where the felt collar would have sat instead of finding a repair sleeve.
It turns out that the pinion seal (Old P/N CR 3653618) is a fairly universal seal size that GM used into the 1980s, so I was able to cross reference it to CR25970 / National 411330N
Fun fact about the pinion nut: it it 1 1/8 -18 thread, which is finer that 12 threads per inch specified by the UNF standard. Turns out it is another standard referred to as extra-fine (UNEF) threads, and special taps and dies are available if, say, you wanted to chase the threads.
The vacuum shifter had some oil inside, likely from the axle, but that washed out with some varsol. There was another oil seal inside here with the old P/N CR 374534. I cross referenced that seal to SKF 9960. There are some felt packing just below the oil seal that I am unsure of how to approach. I will probably just clean it as best I can and reinsert into the housing.
